This invention relates to an improved process for removing hydrogen sulfide from fluid streams. In another aspect, this invention relates to a composition suitable for use in such process. A further aspect of this invention relates to an improved method for the manufacture of a sulfur sorbent suitable for use in the removal of hydrogen sulfide from fluid streams.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be released as a waste stream, removal of sulfur from the fluid stream can be necessary to meet the sulfur emission requirements set by various air pollution control authorities. Such requirements are generally in the range of about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur sensitive catalysts or to satisfy other process requirements.
Traditionally, sulfur sorbents used in processes for the removal of sulfur from fluid streams have been agglomerates utilized in fixed bed applications. Because of the various process advantages from the use of fluidized beds, it can be desirable to utilize a fluidized bed of zinc oxide based sorbent in the removal of sulfur components from fluid streams. There are, however, a number of problems associated with the development of the use of fluidized beds in sulfur sorption that, prior to the discovery of the invention described herein, have not been resolved. Particularly, conventional methods for the production of fluidizable materials have necessarily required spray drying techniques in order to obtain particle sizes in the fluidizable range and to obtain the sufficiently spherically shaped particles thought to be necessary for fluidization. Spray drying techniques, however, have drawbacks due to their relatively high cost and comparatively low production capacity. It would be desirable to have a method for economically producing a fluidizable sorbent material without resort to costly spray drying techniques and to utilize the advantages of a fluidized bed in the removal of sulfur compounds from sulfur-containing fluid streams.
Another concern associated with the use of fluidizable materials is the attrition losses resulting from the fluidized particles colliding with each other and with the equipment walls which define a fluidization zone that contains the fluidized bed. It is desirable to keep attrition losses of the sorbent as low as is possible in order to minimize replenishment of the material and disposal requirements. The attrition resistance of a fluidizable material provides a measure of the weight loss of the fluidizable material when it is used under the harsh operating conditions of a fluidized bed.
While fluidized bed reactors can provide benefits over other types of reactors, such as fixed bed and moving bed reactors, they still present certain disadvantages. Among them are the capital costs associated with the special equipment required for operating fluidized bed reactors. Another disadvantage of the use of fluidized bed systems in sulfur sorption is the need to use diluted air for regeneration of a used sulfur sorbent.
A transport reactor system can be a desirable system for use in the removal of hydrogen sulfide due to the lower capital costs associated with such system. However, the effectiveness of a transport reactor system is substantially dependent upon the sorbent used in the system. The sorbent must have the physical properties that make it circulatable while still having properties suitable for use as a sulfur sorbent. To be circulatable, the sorbent must be able to be fluidized within a fluidization zone by a fluid stream and to be conveyed within such fluidization zone against the force of gravity at high linear velocities, and it must also be circulatable within a transfer zone in the direction of gravity but at linear circulating velocities significantly lower than those within the fluidization zone. Only sorbent particles with certain specific properties are circulatable within a transport reactor system.